Water-resistant adhesive



Patented Mar. 14, 1939 PATENT OFFICE WATER-RESISTANT ADHESIVE George M. Shisler and Elmer Bergey, Lansdale,

Pa., assignors to Perkins Glue Company, Lansdale, Pa., a corporation of Delaware No Drawing. Application February 5, 1936, Serial No. 62,546

7 Claims.

particularly suitable for use in the wood-working industries, and more particularly it relates to a novel water-resistant glue of the general type known as casein-lime-soda glue.

7 One object of the present invention is to provide a glue of the type generally known as caseinlime-soda glues, the glue of the invention possessing not only the necessary properties making it adaptable for use in the wood-working industries, but also novel and advantageous characteristics not previously encountered in the glues of this type.

A further object of the invention is to furnish a glue of the general type known as casein-limesoda glues possessing a relatively prolonged permissible assembly period, without the veneer or joint strength falling below safe values, so that a period of one hour or longer may elapse between the operations of spreading the glue and applying the pressure, which property is of great commercial value since it increases greatly the iool-proofness of the veneering operation.

Still another object is to provide a wood-working glue which is particularly adapted for use in hot-pressing operations, due in part to the property of permissible-delayed assembly, and in part to the fact that a semi-moist glue film is. formed upon gelation while the bulk of the moisture is uniformly disseminated throughout the massoi the veneer, and is thus available for heat transfer and steam-curing, although there is also present immediately at the glue film suflicient moisture to produce a satisfactory and neat fluxing under the influences of heat and pressure.

It is also an object of our invention to provide an adhesive in which there is less tendency toward penetration and stain on moderately th'in veneers, and in which the glue line is less severe on cutting tools, than is the case with the glues now generally available.

- Furthermore, it is an object of the invention to furnish an adhesive possessing a relatively prolonged permissible assembly period, andv an adhesive which may be produced more economically than the adhesives of the same general class now on the market, the novel adhesive, however, having satisfactory properties including water-resistance and strength of dried glue fabric, as demonstrated by wet and dry shear tests.

Other objects of the invention will be apparent from a consideration of the specification and claims.

Wood-working adhesives prepared from mixtures of casein, lime, and varioussodium salts,

Our invention relates to an improved adhesive,

particularly sodium salts of weak acids, or of acids which form a relatively insoluble salt with the lime, with or without the addition of small quantities of oils and other substances,- havev long been known and used. These adhesives are 5 known as casein-lime-soda glues and are particularly employed in the wood industries; for example, in the manufacture of veneered products. The adhesives contain casein which is a relatively expensive ingredient, and hence the 10 cost of the glue is relatively high. Furthermore, with these glues, it is generally imperative to subject the assembled bale to pressure within 10 to minutes after application of the glue, the time depending on the amount of glue spread on 1 the wood, the moisture content of the wood and the like. This short permissible assembly period is a disadvantage in many instances, particularly in hot-pressing operations, since time is not permitted to plan the pressing operation in the 20 most eflicient manner. Furthermore, there is a tendency of these products to penetrate and stain thin veneers, and the glue line is severe on cutting tools.

The product of the present invention is su- 5 perior to the previously available glues and the disadvantages thereof are overcome to a great extent, for example, as much as 1 or 2 hours or more may elapse between the spreading of the glue and the application of the pressure. Our inwhole or in part therefor, and an alkali metal hydrate or salt, such as a sodium or potassium salt of a weak acid, or of an acid forming a dimcultly soluble lime compound, so that caustic soda is formed upon reaction. The alkali metal substances will be included with the term alkali 'metal'substance capable of furnishing alkali metal hydrate. Mixtures of various sodium and/or potassium salts may be advantageously employed, and small amounts of mineral m vege- .table oils, albumens and vegetable globulins may be added to impart somewhat modified characteristics, if desired. Carbon disulphide, for example from 1% to;6%.by weight of the dry glue powder, may be ed to advantage where an especially water-resistant product is desired.

acid casein are present.

The ordinary dried milk of commerce employed may be dried whole milk, as well as dried skim milk, but since the latter is a cheaper product, and functions entirely satisfactorily, it will be employed in most instances. The total amount of dried milk used with the casein will depend on the properties desired in the adhesive, but in general the total of these materials, on the basis of the dry glue powder, will range between 50% and 75%. The dried milk may be present in relatively small proportions, for example, as low as 5% based on the casein employed, or may be greatly in excess of the casein employed. Very satisfactory results are obtained when the dried milk employed varies from 20% to 200% on the basis of the casein used, the length of the permissible assembly period, increasing in general as the content of dried milk. increases. Products with optimum desired characteristics are obtained when the casein is present between and 70%,preferably between 15% and 55% and 4 dried milk is present between 5% and 50%, preferably between 15% and 50% based on the dry glue, the total amount of casein and dried milk ranging between 50% and 75%. It is also oftentimes desirable to have albumen present in amounts between 3% and 10%. I

The ordinary dried milk of commerce obtained in powdered form, as it is available on the market, is preferablyemployed, andthe glue may be-made up as a mixture of the dry ingredients, and stored and shipped in this form to the customer who adds the required amount of water thereto when the glue is to be applied. Alternately, the glue may be prepared by adding the various ingredients separately, or in groups, directly to the water. In either case, the resulting gluewater composition is substantially the same in properties. Hence, in this specification and the claims, where the glue of the present invention is referred to, it is to be understood that both the dry powder and the powder-water mixture are included.

The'advantagcous properties foundin the ad- I hesive' of the present invention are probably due in part to the difference in the nature of the albuminous and other materials in dried milk and in casein, and in part to the materials present in the dried milk which are absent in casein. Commercial casein is'obtained by the acid precipitation of the casein, from liquid milk, either by the so-called acid-cook, the acid-precipitation or the self-souring process. Since this casein is prep ed under hydrolyzing conditions, many of the intra-molecular linkages are weakened or openedup. On the other hand, dried milk is obtained under dehydrating conditions causing the linkages to be drawn more closely together resulting in at least some linkages that are irreversible. Commercial casein consists of free or acid-casein, with marked acid properties. The casein of dried milk, however, is combined with various bases,

such as potassium, calcium, sodium, which are also linked up with phosphoric acid, perhaps simply by an exterior valence, or perhaps more intricately in such a way that the phosphate is interior between. portions of the protein molecule itself or between an amino group of the protein molecule and some naturally occurring, organic,

basic wetting agent normally present in'milk.

Furthermore, the aggregation of the other dried milk elements, such as albumens, globulins, and sugars adjacent to. or possibily combined with, the crude casein elements in the dried milk influences the properties thereof. These materials, are either not associated with commercial casein or are present in a different form; for example,

casein is practically free from lactose and other sugars. The presence of the sugars in the dried milk manifests itself in the gel formed by the glue of the present invention. Since, either due to chemical setting or to the absorption of water by the woodstructure, the gel is covered by, and is intimately associated with a sticky exudate, probably comprising lactose solution and alkalidecomposition products of lactose, inconjunction with globulins and albumens contained in the .milk. The water contained in these dispersions surrounding the casein particles protect the casein from the lime, and prevent the combination from causing an immediate irreversible set; that is, it stabilizes the casein-lime hydrosol until the glued joint is considerably dried out. This semi-moist glue film is particularly adapted for hot-pressing operations, since, while the bulk of the moisture is quite uniformly disseminated throughout the mass of the veneer, and is thusavailable for heat transfer and steam-curing, there is also present immediately at the glue film, suflicient moisture to produce a neat fluxing under the influences of heat and pressure. n

A further characteristic of the gel of dried milkcontaining glues is the feature of progressive increase in firmness, when relatively large amounts of alkali are used. This feature is observed ina slightly different way with the abnormally long period of hardening-during intense drying of the glue film and is also observed in a pronounced increase in wet-shear strength upon hot pressing. These manifestations of increased rigidity may, perhaps be attributed in part to the removal of alkali by acid derived from the decomposition of lactose, and in part to aldehydic orcarbonylbearing compounds from the same source acting upon the various proteins and protein-residues contained in the) glue mixture.

These reactions are also probably enhanced by the presence of oxygen'and are accelerated by temperatures obtained in the hot-pressing or other curing processes brought about by the influence of heat.

Many of the glues containing dried milk also have the property of forming a quick 'gel when a small portion of the water of the glue mixture is removed, so there is less tendency toward penetration and stain on moderately thin veneer. The presence of lactose renders-the glue line more easily cut and less severe on cutting tools.

The glues of the present invention, when first prepared, are very pale yellow, the shade becoming progressively deeper with time, and eventually a deep yellow or orange product is formed. Casein glues of the same alkali composition, however, are white. The glues of the invention, containing both dried milk and casein, become rosepink upon standing overnight, which coloration is more pronounced in glues formulated with a high percentage of tri-sodium phosphate or other salts yielding similar pH values.

Thus, it is seen that commercially precipitated or acid casein, and the casein content of dried milk, which is casein dehydrated in the dispersed condition in association with naturally occurring milk substances, are alike in name only, and that,

the substances are, in fact, chemically and potentially vastly different, imparting different properties to adhesives of the casein-lime-soda type. Many of the properties of the glues of the invention are superior to those previously obtained, and while hereinabove, certain theoriaa have been suggested to account for the improvements in the properties of the glues, it is to be understood that the invention is not to be limited thereby, as the results may be due to other chemical conditions or reactions.

The following are typical examples of the adhesives of the present invention:

Example 1 Percent Casein 54 Ordinary dried milk of commerce--- 15 Hydrocarbon oil l Hydrated lime 16 Sodium-fluor 3 Tri-sodium phosphate 6 Soda ash 5 The ingredients are mixed together dry to obtain an intimate mixture which is added to cold water in the ratio of one'part glue-powder to two parts water by weight, the water being agitated during the addition. After a lapse of 20 to 30 minutes an adhesive, smooth, fluent glue results with excellent strength and water-resistance. If desired, the water-resistance of the glue may be still further improved by stirring into it, 1.5% to 2.0% carbon disulphide after the glue solution is This glue iscdry mixed and brought into solution with 2 parts of water by weight, as in the glue of Example #1. After 20 to 30 minutes it is ready foruse, and is satisfactory as a glue for the wood-workingtrade.

Example 3 I Percent Casein 24 Ordinary dried milk of commerce 44 Mineral oil 1.5 Pine oil 1 Hydrated lime 16.5 Sodium fluor Y 3 Sodium carbonate l l 10 This glue is dry mixed as is the glue of Example #1. The glue solution may be made using 2 to 2.25 parts of water by weight. When 2 parts of water are used a smooth heavy glue results, which gels when a small amount of water is removed by absorption by the veneer, and alkali penetration and stain is very greatly minimized.

Example 4 a Percent Casei I 20,: Ordinary dried milk of commerce- 38 Blood album 5 Mineral oil 1.25 Pine .75 Hydrated lime 14.5 Sodium fluoride 2:5

1 hydrate, ordinary dried basis of the dry glu .saltfurnishinacausticcoda.ordinary This glue is dry mixed as under Example #1. The wet mix is made by adding 1 part dry-glue powder to about 1.8 parts of cold water by weight.

A glue of excellent wet and dry strength results. At the same time it is very easy on cutting tools.

Ez cample 5 Percent Casein 25 Ordinary dried milk of commerce 45 Floor o I f 2 Time 16 Sodium fluoride 12 These materials are dry mixed and then dissolved in 2 to 2% parts water. After 20 to 30 minutes a satisfactory wood glue results.

Example 6 A mixture of 34 parts of commercial casein and 66 parts of dried milk is prepared. This mixture is added to 300 parts by weight of water and after the and softened, 7 to 14 parts of lime suspended in 20 to 30 parts of water'are added thereto under conditions of constant stin'ing. After a minute or two, 9 parts of caustic soda, dissolved in about 36 parts of water are added to complete the dispersion of the calcium-protein complexes. After about 5 minutes, a good glue is obtained. The water resistance of'the product is still further improved by the addition of 1% to'5% of carbon disulphide on the basis of the weight of dry protein-bearing materials. If desired, the lime and caustic soda may be added in one sus-' pension.

Considerable modification is possible in the percentages of materials employed, as well as in the alkaline earth hydrates and the alkali without departing from the invention.

20- proteinaceous mass has swolienl ,metal compounds selected, and in the methods 1. A glue of the casein-lime-soda type possess-'- ing a relatively prolonged permissible assembly period and comprising an alkaline earth hydrate, an alkali metal compound furnishing alkali-metal ing a relatively prolonged permissible assembly period and comprising hydrated line, a sodium salt furnishing causticsoda, ordinary dried milk of commerce, acid-casein, and carbon disulphide, the dried milk and'acid-casein being present in amounts fr'om 50% to on the basis of the d glue,

thedriedmilkbeingfromfiqt t0200% of the casein present, and being present in'amounts from 1% to 6% on thebasis ofthedryglue.

4. A glueof the casein-lime-soda typ sa l vel r lonsed permis ble period and comprising hydrated lime. a sodium.

a sodium the carbon disulphide drlcdmilk milk of commerceand 4 w v 9,150,940 I or commerce, and acid-casein, the caeein belng present from 15% to 70% and the dried milk beingpreaenttrom5%to50%basedonthedry glue, thetotnl amount 01' casein and dried milk being between 50% and 75%.

5. A glue otthe casein-lime-sodn typepoeausing a. relatively prolonged permissible 1y periodandhydrated lime,acodium salt furnishing caustic eodmordinnry dried milk 'otcommercenndncid caeeImthecueinbeing present from 15% to 55%, and the dried milk being present between 15% and buedon the dry glue, the total amount of caaeinund.

' otcommerce, acid-casein and albumen, the casein being preeentirom 15% w the dried milk from 15% to 50%, and the albumen from 3% to 10% based on the dry glue, the total amount of casein-and dried milk being between 50% end.

7. A glue of the casein-lime-soda type possessing a. relatively prolonged permissible assembly period and comprising hydrated lime, a sodium salt, ordinary dried milk 01' commerce, lcidcaeein, albumen and carbon disulphide, the casein being present from 15% to 55%, the dried milk from 15% to 50%, the albumen from 3% to 10%, and the carbon disulphide from 1% t0 5% based on the dry glue, the total amount of GEORGE M. SHIBLER;

casein and driedmilk being between 50% end 

